Centrifugal casting of metals



May 24. 1927.

1.. I. YEOMANS CENTRIFUGAL CASTING 0F METALS Filed Juiy 17, 1924INVENTOR.

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' Z W lay g 6 I ATTORNEYS.

Patented May 24, 1927.

UNITED STATES PATENT OFFICE.

LUCIEN I. YEOMANS, OF CHICAGO, ILLINOIS, ASSIGNOR TO A. 0. SMITHCORPORATION, OF MILWAUKEE, WISCONSIN, A CORPORATION OF NEW YORK.

CENTRIFUGAL CASTING OF METALS.

' Application filed July 17,

The features residing in the invention will now be described, and thenovelty thereof will be pointed out in the-appended claims.

The drawing herewith is merely illustra- 6 tive in a conventional mannerof the uses of my invention, which latter it will be understood may beemployed in connection with or applied to any type of centrifugalcasting machine in which a rotating metal mold 10 is used. However, theinvention is not to be limited in its application to that particularbranch of the art, but may be employed as well in connection with metalmolds used in ordinary casting processes.

In the drawing which accompanies this specification, Figure lshows alongitudinal, vertical sectional view, and Fig. 2. shows an endelevation, looking from the right of Fig. l, of a conventionalcentrifugal casting machine, provided with a tubular mold havingtheusual removableheads, one of which at least is formed with an enlargedcentral opening through which the molten metal used in casting may beintroduced, and which may be removed'therefrom to permit the casting toSuch a mold being old and well known,

specific description of its structural features is unnecessary .in thepresent instance.

It is recognized in the present art that the process of centrifugalcasting with metal molds is particularly well adapted to the expeditiousproduction of annular or tubular metal bodies, designed for and capableof various used, within'a limitedrange. Pespite the fact that theprocess of centrifugally casting metals has been known andoperated invarious manners and with variously constructed machines for more thanone hundred years, such process has not yet attained that high degree oferfection in its results that is greatly to be esired in an art soreplete with dormant possibilities. The causes which have intervened toprevent the achievement 'of the results sought for are many, and havebeen the subject of much study and wide experimentation in the attemptsof inventors to solve the problems which are involved.

Principal among these causes is the matter of the control of the thermalconditions attending the use of the metal mold during successive castingoperations. To create and maintain a suitable thermal condition in themetal moldused in successive casting operof the casting.

peated use of the mold in successive casting-v be withdrawn from themold.

1924. Serial ml 726,445.

as a normal condition, has proven a vex-atious problem. it has; been thesubject of much theoretical work, only partially productive of theresults which have been earnestly striven for.

In casting metal alloys which are susceptible to a quick chilling effectupon contact with the relatively cold surfaces of a metalmold, theheatis abstracted very rapidly from the casting after the freezing point ofthe metal alloy has been reached, very often to the deterioration of thequality On the other hand, the reoperations where rapid production isdesired, has the effect of creating in the mold a temperature whichbecomes so high that it approachesthe fusion point of the metal'of whichthe mold is formed, and contacting portions of the molten metal which ispoured into the mold will stick thereto, resulting in defective castingsand renderingthe mold unscrviceable until it can be restored to primecondition. Again, such high temperature in the mold is a source ofdanger, -in that the cohesive nature of the metal of the mold isdisturbed, and the latter is liable .to disruption under the centrifugalforce generated inthe high speed rotatlon of the mold. The eliminationof these adverse conditions is the purpose of my present invention.

I In making relatively thin castings of any metal by the centrifugalprocess, it is of material advantage to retard the cooling of thecastingto an extent which will permit all gases and lighter impuritiesor other inclusions in the molten metal to escape with certaintybeforethe metal congeals, and it has been found'that superior results may beobtained by retarding this chilling of the cast ing as much as possibleand protracting the interval duringwhich a given amount of heat istransferred from the casting to the mold, or through the mold to thecooling media sometimes resorted to in conjunction therewith. 1 -Amongthe plans looking to that end, various metals have been used in theformation of the molds. Molds have been constructed, some of costlymetals having a property of internal conductivity which is these moldsof the better quality have been mold at the time ,found to conduce tothe production of markedly superior results in the castings. By reasonof such superiority, it has been found profitable to use such molds,although their first cost has been excessive, when compared with thecost of other metals having greater internal conductivity.

In my studies and tests along th1s lme, conducted with a view to theascertainment. of a satisfactory solution of. the difliculties whichhave been encountered in so many instances in the ast, I have discoveredthat by a very simpl d rooedure the thermal condition ofa metal mold maybe brought to such desired normal temperature as will be best 7 adaptedfor and conducive to the achievement of highly satisfactory results in.successive casting operations, and that such normaltemperature can bemaintained efii ciently throughout the whole of the casting operations,by reducing to a predetermine degree the temperature of the mold, as bythe abstraction therefrom of 'a' definite number of heat unitstransmitted to the mold by the molten metal in the casting operation.

This very desirable result is brought about by a. novel treatmentapplied to the mold in the interim of the casting operations. In suchtreatment, I find it entirely possible to control the rapidity withwhich the heat is.

abstracted from the casting 'metal" by 'the mold, when the molten metalused in cast-- ing is poured thereinto. -As hereinbefore indicate thisstate of affairs follows treatment of the mold after each castingoperation, so that the temperature of the mold at the time of pouringthe metal is maintained in such normal degree as will surround thecasting operations with conditions contributing largely to theproduction of wholly satisfactory articles of uniform construction inthe successive casting operations. The extent of the absorption by themold of the heat of the cast 2: metal and the temperature which the moldcan attain, are regulated with such substantial exactness that materialvariations in the temperature of the of casting are practicallyeliminated. Hence, the mold is uniformly conditioned at all times ofcasting, so that the transmutation of the molten metal into a casting isretarded in such degree as is necessary to Hermit its conversion into asolid state who y free from blow holes or impurities of any nature.

conditioning the mold so as 'to present a.

predetermined temperature reduction for the purposes of my invention, Iuse water as a temperature equalizer or quencher. But the manner of itsapplication is distinctly novel, and the provision of specialconstructions 'for the circulation of water through or about the mold,or the submersion of the latter, as are sometimes resorted to, isrendered.

unnecessary. Thus, I am enabled to dispense with all of the usualextraneous water' cooling devices' and their connections, to-

gether with the costs required for their installation. Such specialconstructions as have been employed heretofore for the purpose ofcooling the mold act with varying degrees of success,'and have not beeneffectlve 1n producing that normal condition in the temperature of themold that is essential to the attainment of the highest results incasting.

4 By supplying a predetermined, -measured quantity of water to theinterior of the mold a the water at the time of its introduction into.the mold to the boiling point, plus the latent heat to transform itfrom water at 212 F. to steam at 212 F.

An example of the application of my invention in a practical manner isillustrated in the following: In casting an annular body of steel havinga wall thickness of one inch and a weight of one thousand pounds, forinstance, a mold having a wall thickness of three inches and a weight ofapproximately three thousand pounds will be provided. The molten metalis cast at a temperature of about 2700 F., and it is desired to removethe casting fromthe mold after congelation at a' temperature of about2000"F., 'or after a drop of about 700 F. in the temperature of thecasting has taken place. The heat transferred from the cast metal to themold may be represented, since the spegific heat of themetal may beassumed as .20,

'(60 1000)=200,000 B. t. u.

In the equation, the factor 60 is'the B. t. u. representing the latentheat of fusion of steel. This total of 200,000 B. t. u. is theequivalent in amount to that represented by the transformation orconversion of 179.3 pounds of water at 62 F. to steam at 212 F., or of21.6 gallons of water at the same temperature so utilized, as follows:

approximately 233- F. .at this time. The

temperatures found to be suitable in the rotating mold after thecooling'operation and before casting, may range from 250 F. to 1100 F.,butshould not be permitted to rise above the latter, in the interest ofsafety while the mold and its charge of molten metal are under rotation.In the present instance, a mold temperature of about 500 F. is suitable,and this is produced by treatment of the mold and maintained as-anormal.

Upon replacing the end plate of the mold after withdrawing the casting,water to the amount of 21.6 gallons will be poured into the rotatingmold, and upon complete vaporization of the water, the temperature ofthe mold will have been reduced about 233 F., or to normal, due to theabsorption of the heat from it necessary to heat and vaporize the water.After which the mold is ready for another casting operation.

These operations are repeated throughout the successive castingoperations, with the result that castings of remarkable uniformity andperfection are produced. lVith these facts in mind, the efi'ect'of theintermitting or alternate casting and cooling of the mold to maintainthe temperature of the latter at approximately a predetermined normaldegree, and their eifect upon the castings produced, as well as upon themolds, are obvious.

I have found it very advantageous in the treatment of the mold incidentto the cooling operation, to introduce a refractory material of suitablenature, for insulating purposes. Suchmaterial may be incorporated in thewater used for cooling and be evenly deposited over the surface of themold when the water is evaporated. Or it may be introduced into the moldas a spray over the surface thereof. The coating may be of a substance,graphite, for example, which will lower the melting point of the metalupon its first contact with the surface of the mold, so as to retard thecooling of the metal, and by alloying with the first. thin layer of themolten metal flowing into the mold, form' upon the casting a surfacewhich will be free fromthe' cracks which are usually attendantupon'processes of casting in whichthe sudden chilling of the moltenmetal under such conditions is productive of or conducive to theproduction of shrinkage cracks which detract from the value of theproduct.

The mold should be pre-heatedto raise its temperature to normal, as apreliminary to the first casting operation. Such. preliminary heatingmay beefl'ected in various ways, as by placing themold in a heatingfurnace, or by subjecting it to a gas flame. Heating maybe eifected alsoby pouring into the mold a quantity of molten metal so as to transfertheheat therefrom to the mold, and such metal may be withdrawn from themold and discarded when this has been done.

Having thus described my invention, what i prises the step ofintroducing into the mold after the casting has been willulraun ameasured quantity of water which by its evaporation will'abstract fromthe mold the heat units imparted thereto by the [molten metal of whichthe casting is formed.

2. In n'ietal casting, the process of mold conditioning which comprisesthe sleps ol heating the mold preparatory to the first casting operationto impart a. normal tem: perature thereto, and after each castingoperation introducing into the mold a measured quantity of water whichin its evaporation will abstract from the mold the heat units impartedthereto by the molten metal, whereby such normal temperature ismaintained;

3; In metal casting, the process of mold preparation which comprises-theoperations of introducing into the mold a measured.

quantity of water which by its evaporation will abstract from the moldthe heat units imparted thereto by the molten metal preof congelation,and restoring the normal temperature of the mold bythe applicationtherein of a measured quantity of water which in its evaporationwillabstract from the mold the heat units imparted thereto by thefinolten metal.

5. In connection with the process recited inclaim 4, the step ofrotating the mold during the operation of pouring the molten metal toform the casting.

6. The process of metal-casting, which comprises the operations ofpre-heati-ng the mold to a pre-determined normal temperature, pouringmolten metal into the mold, withdrawing the casting after thetemperature has reached the point of congelation, and restoring thenormal temperature of the mold by the application of a measured quantityof waterwhich in its evaporation will abstract from the mold the heatunits imparted thereto by the'molten metal.

7. In connection with the process recited in claim 6, the step ofrotating the mold during theoperation of pouring. the molten metal toform the casting.

8. The process of metal casting which comprises the o erations ofpre-heating the mold to a pre-dhtermined normal temperature, coating theinside of the mold with a 5 material which will retard the cooling ofthe casting metal and form an alloy with the surface ofthe metal ofwhich the casting is formed, pouring molten metal into the mold,withdrawing the casting when its 10 temperature reaches the point ofcongelation, and restorin the normal temperature of the mold by tlieapplication of a measured quantity of water which in its evaporationwill abstract from the mold the heat units imparted thereto by themolten metal. ll

9. In connection with the process recited in claim 8, the step ofrotating themold during the operation of pouring the molten metal toform the casting.

In testimony whereof, I have signed my 30 name at Milwaukee, Wisconsin,this 3d day of July, 1924.

LUCIEN I. YEOMANS.

